THE STRUCTURE OF IN-SITU ICES III AND V. C. Lobban¹, J.L. Finney¹ and W.F. Kuhs², ¹Dept. of Physics & Astronomy, UCL, London WC1E 6BT. UK, ²MKI, Universitt Gttingen, D-37077 Gttingen. Germany

The degree of hydrogen ordering within ices III and V is controversial, very little structural work having been done on these phases under their stable conditions of high pressure. Instead samples have generally been quenched to liquid nitrogen temperatures and recovered to ambient pressure, the results of such structural studies differing from conclusions drawn from dielectric, calorimetric and spectroscopic measurements under pressure. We have previously attempted to study these phases under pressure using a helium gas pressure system. However, the helium diffused into the system forming helium hydrate, resulting in great difficulty in forming the desired ice phases. More recently, during an experiment designed to look at argon clathrate, under argon pressures of up to 5kbars, we found that temperature reduction under pressure led to the formation of ice V rather than the clathrate. As starting from the liquid led to a very poor powder, more recent work has established that ices III and V can be prepared from powdered ice Ih, again under argon pressure. We have already collected one data set on ice III under pressure which clearly shows a small amount of partial ordering. We also have two experiments scheduled for the study of these systems on HRPD at ISIS and D2B at ILL. Structural refinements will be presented from all these experiments, with particular emphasis on the hydrogen orderings in the two phases.